1. Field of the Invention
The present invention relates to a numerically controlled wire-cutting electric discharge machine, more specifically, a machine which cuts a piece of work by a discharge which is produced in a small gap between the piece of work and a wire electrode which is passed through a small hole provided in the piece of work.
2. Description of the Prior Art
In the conventional wire-cutting electric discharge machine, the wire electrode is rolled and displaced from one reel to another reel in a stretched condition, and a small discharge gap is formed between the wire electrode and the piece of work which is placed at an approximately right angle to the wire electrode. Liquid such as water or oil is supplied to the above-mentioned small discharge gap and working electric pulses are repeatedly supplied between the piece of work and the wire electrode, so that the piece of work is cut in accordance with a locus which is formed by the relative displacement between the wire electrode and the piece of work. When we assume that the displacement of the wire electrode is carried out in two directions, the piece of work is cut or extracted by feeding the piece of work in an X axis and a Y axis direction at a right angle to a Z axis.
In the above-mentioned wire-cutting electric discharge apparatus, a pair of dies are conventionally used for holding a wire electrode. However, it is very troublesome for a workman to pass the wire electrode through the pair of dies. For solving this problem, a pair of V type slot guides, which are provided with a V type slot, are used so that the wire electrode can be easily stretched. However, when we use the V type slot guides, in some relative displacements between the piece of work and the wire electrode, the wire electrode is forced out of the V type slot guides. Therefore, the holding condition of the wire electrode in the V type slot guides becomes unstable and highly accurate cutting cannot be carried out.
For obviating the above-mentioned drawback, a means for closing the V type slot after setting the wire electrode in the V type slot guide is conventionally used. However, it is difficult to stretch the wire electrode because of the existence of the above-mentioned closing means.